Aspects of this invention were made with government support of the National Science Foundation, grant number BES9986296. Further support has been provided by Texas Higher Education Coordinating Board, grant number BER-ATP-253. Accordingly, the government may have certain rights in this invention.
1. Field of the Invention
The present invention relates generally to biomedical engineering, imaging, medicine, and medical treatment. More particularly, it concerns clinical laser treatment of cutaneous vascular lesions using chemical agents that not only increase light penetration but also decrease blood flow velocity.
2. Description of Related Art
Cutaneous vascular lesions can be classified into two main categories. The first includes benign disorders, such as the hemangioma (a benign tumor consisting of a dense mass of blood vessels) and the cutaneous nevus (a congenital discoloration of a skin area, also called a strawberry or stork mark) [van Gemert et al., 1995; Mulliken, 1992]. The second category is made up of vascular malformations, where the lesion is caused by abnormal blood vessel pathology [Mulliken, 1992]. Included in this class of cutaneous vascular lesions is the port wine stain (PWS), a congenital lesion in which ectatic capillaries make an area appear a dark red color and produce raised nodules protruding above the normal skin surface. Another vascular malformation is leg telangiectasia, small, localized clusters of blood vessels sometimes found deep (millimeters) below the surface. Telangicctasis can also occur as an extensive network that is much more widespread [Goldman, 1992].
Some of these lesions, such as the port wine stain (PWS), can be quite traumatic for a patient, resulting in serious psychological and social problems [Lanigan et al., 1989; Tan, 1992; Morelli et al., 1992; Masciarelli, 1992; van Gemert, 1992]. When lesions are located near joints, lips, or the eyes they can also interfere with normal functions and lead to serious problems such as hypertrophy of skeletal tissue or more severe conditions [Mulliken, 1992]. Because the lesions become increasingly hypertrophic, early treatment is preferred.
Currently, the only accepted treatment for these vascular lesions is pulsed laser radiation at selected wavelengths that target the absorption characteristics of hemoglobin. By selecting the proper laser pulse duration, the process is referred to as selective photothermolysis. Blood vessels are damaged by the increase in temperature resulting from absorption of pulsed laser light. The objective is to permanently destroy the blood vessels comprising a cutaneous lesion, while sparing surrounding skin structures.
A number of shortcomings exist in current clinical treatments due to the lack of parameter optimization and sufficient delivery of light to deep lying blood vessels. Unfortunately, because the treatment parameters governing the effectiveness of laser therapies vary greatly from patient to patient, many instances of incomplete destruction of abnormal vessels and clearing of the lesion occur.
In general, low treatment success rates remain a problem with existing laser treatments of vascular lesions. This low success rate is due to at least two main limitations: (a) restrictions in the achievable penetration depth of light in biological tissue and (b) insufficient increase in blood vessel temperatures associated with high flow velocities.
The first limitation (limitation (a)) in the laser treatment of cutaneous vascular lesions involves rapid attenuation of incident light with depth. Attenuation of laser light in biological media occurs by absorption and scattering. In many cases, deep blood vessels in a lesion are not sufficiently heated by incident light due to competition from absorption and scattering by other tissue constituents. This competition for laser light decreases the fluence rate [W/cm2] available for photocoagulation of a blood vessel. In view of this limitation, methodologies that decrease light attenuation and increase the penetration depth of incident light are desirable.
The second limitation (limitation (b)) in the laser treatment of vascular lesions involves the lack of control of blood flow velocity. Blood flow velocity has been shown to be an important factor that affects the success of vessel photocoagulation. Specifically Boergen, et al. have shown that complete flow cessation of blood in vessels before laser irradiation significantly decreases the fluences required to permanently destroy a blood vessel [Boergen et al., 1977]. Despite this realization, current laser treatment techniques have not been able to fully capitalize upon the benefits afforded by controlling blood flow velocity during treatment. In view of this limitation, methodologies that not only decrease light attenuation, but also decrease blood flow velocity would be desirable.
The referenced shortcomings of conventional methodologies mentioned above are not intended to be exhaustive, but rather are among many that tend to impair the effectiveness of previously known techniques concerning the laser treatment of cutaneous vascular lesions. Other noteworthy problems may also exist; however, those mentioned here are sufficient to demonstrate that methodology appearing in the art have not been altogether satisfactory and that a significant need exists for the techniques described and claimed herein.